CaO Precursors Research Articles

Role of calcium looping conditions on the performance of natural and synthetic Ca-based materials for energy storage

In this work, the multicycle activity of natural CaO precursors (limestone and dolomite) and Ca-based composites (Ca3Al2O6/CaCO3 and ZrO2/CaCO3 mixtures) has been studied for Thermochemical Energy Storage (TCES) in Concentrated Solar Power (CSP) plants by means of the Calcium-Looping process (CaL), using two integration schemes proposed elsewhere that differ in the calcination stages. Under CSP-He conditions, calcination for CaO regeneration is performed under pure He at low temperatures (725 °C) while under CPS-CO2 conditions calcination is carried out under pure CO2 at high temperatures (950 °C). The latter avoids the use of selective membranes to separate He from CO2 even though it requires the use of more expensive materials for solar receptors. Carbonation/calcination conditions drastically affect the multicycle CO2 uptake of the materials tested. Effective multicycle conversion is higher in CSP-He tests due to the mild conditions employed for calcination, which mitigates CaO sintering. On the other hand, the harsh calcination conditions used in CSP-CO2 tests enhance sintering of CaO derived from limestone and the Ca3Al2O6/CaCO3 composite due to the low Tammann temperature of Ca3Al2O6. CaO sintering is hindered by the presence of inert oxides with high Tammann temperatures, such as ZrO2 in the ZrO2/CaCO3 composite and MgO in dolomite. Dolomite derived CaO shows high effective conversion values along the carbonation/calcination cycles when tested under both types of conditions, as compared to limestone and the composites, which suggests that the integration scheme based on CSP-CO2 conditions would be a feasible alternative to CSP-He if natural dolomite were used as CaO precursor.

Highly Porous Sr/Mg‐Doped Hardystonite Bioceramics from Preceramic Polymers and Reactive Fillers: Direct Foaming and Direct Ink Writing

Novel hardystonite‐based bioceramics are obtained by thermal treatment, in air, of silicone resins and reactive fillers. Using commercial silicones embedding SrO and MgO precursors, in addition to CaO and ZnO precursors, a quite complex solid solution (Ca1.4Sr0.6Zn0.85Mg0.15Si2O7) can be achieved, at 1100 °C, instead of pure hardystonite (Ca2ZnSi2O7), with improvements in biocompatibility and bioactivity. Highly porous foams are obtained by gas evolution at the early stage of heat treatment (at 300–350 °C), from the dehydration of active filler present in hydrated form (Mg(OH)2). Additionally, direct ink writing of silicone‐based pastes is used for the manufacturing of scaffolds with non‐stochastic pore architecture. In the latter case, strong scaffolds (with compressive strength exceeding ≈12 MPa) are obtained by adding fine glass powders as an additional filler. This addition enhances the viscous flow upon firing, but do not compromise the phase evolution, owing to the exact match in the composition between glass and silicone/filler mixture.

Influence of CaO precursor on CO2 capture performance and sorption-enhanced steam ethanol reforming

This work presents the effect of calcium and carbonate precursors on properties of CaCO3. The synthetic CaCO3 samples were transformed into CaO and tested their application to high-temperature CO2 capture. Four different sorbent precursors were investigated in this work, including calcium chloride (CaCl2) and calcium acetate (CaAc2) as calcium precursor, and sodium carbonate (Na2CO3) and urea (CO(NH2)2) as carbonate precursor. The results show that both calcium and carbonate precursors affect morphologies of CaCO3; CaCO3,Cl-Urea, and CaCO3,Cl-Na have calcite phase, whereas mixed-phases of calcite (30%) and vaterite (70%) are observed with CaCO3,Ac-Na, and aragonite is found with CaCO3,Ac-Urea. CaCO3,Cl-Na exhibits small cubic (rhombohedral) particle, CaCO3,Cl-Urea possesses spherical particle with rough surface, CaCO3,Ac-Na has spherical-like morphology with smooth surface, and CaCO3,Ac-Urea possesses aggregated form of CaCO3 particles. For application to CO2 capture, CaO derived from CaCO3,Ac-Urea provides the highest CaO conversion of 80% at 700 °C. The synthetic CaO-based sorbents were further incorporated with nickel oxide to form one-body bi-functional catalysts for H2 production from sorption-enhanced steam ethanol reforming. The results show that 87%H2 purity could be obtained with pre-breakthrough period of 60 min. Sorbent reactivity can be maintained the production of H2 for at least 10 consecutive cycle tests.

The mOxy-CaL Process: Integration of Membrane Separation, Partial Oxy-combustion and Calcium Looping for CO2 Capture

CO2 capture and storage (CCS) is considered as a key strategy in the short to medium term to mitigate global warming. The Calcium-Looping process, based on the reversible carbonation/calcination of CaO particles, is a promising technology for post-combustion CO2 capture because of the low cost and non-toxicity of natural CaO precursors and the minor energy penalty on the power plant in comparison with amines capture based technologies (4-9 % compared to 8-12 %). Another interesting process to reduce CO2 emissions in power plants is oxy-combustion, which is based on replacing the air used for combustion by a highly concentrated (~95 % v/v) O2 stream. This work proposes a novel process (mOxy-CaL) for post-combustion CO2 capture based on the integration of membrane separation, partial oxy-combustion and the Calcium-Looping process. An oxygen-enriched air stream, which is obtained from air separation by using highly permeable polymeric membranes, is used to carry out partial oxy-combustion. The flue gas exiting partial oxy-combustion shows a CO2 concentration of ~30 % v/v (higher than 15 % v/v typical in coal power plants). After that, the flue gas is passed to the CaL process where the CO2 reacts with CaO solids according to the carbonation reaction. Thermogravimetric analysis show that the multicycle CaO conversion is enhanced as the CO2 concentration in the flue gas stream is increased. Process simulations show that the mOxy-CaL process has a high CO2 capture efficiency (~95%) with lower energy consumption per kg of CO2 avoided than previously proposed post-combustion CO2 capture technologies. Moreover, the overall system size is significantly lower that state-of-the-art CaL systems, which allows for an important reduction in the capital cost of the technology.

Carbonation of Limestone Derived CaO for Thermochemical Energy Storage: From Kinetics to Process Integration in Concentrating Solar Plants

Thermochemical energy storage (TCES) is considered as a promising technology to accomplish high energy storage efficiency in concentrating solar power (CSP) plants. Among the various possibilities, the calcium-looping (CaL) process, based on the reversible calcination–carbonation of CaCO3 stands as a main candidate due to the high energy density achievable and the extremely low price, nontoxicity, and wide availability of natural CaO precursors such as limestone. The CaL process is already widely studied for CO2 capture in fossil fuel power plants or to enhance H2 production from methane reforming. Either one of these applications requires particular reaction conditions to which the sorbent performance (reaction kinetics and multicycle conversion) is extremely sensitive. Therefore, specific models based on the conditions of any particular application are needed. To get a grip on the optimum conditions for the carbonation of limestone derived CaO in the CaL-CSP integration, in the present work is pursued a...

Photocatalyst of Perovskite CaTiO3 Nanopowder Synthesized from CaO derived from Snail Shell in Comparison with The Use of CaO and CaCO3

Calcium titanate belongs to the important group of compounds with a perovskite structure having high dielectric loss for various applications including photocatalysis mechanism. Refer to the principles of green chemistry, in this work preparation of CaTiO3 was conducted by using CaO derived from snail shell. Aim of this research are to study the physicochemical character of perovskite derived from snail shell and its comparison with CaO and CaCO3 as Ca sources. Material preparation was performed by solid reaction of Ca sources with TiO2 under comparison with CaO and CaCO3 precursors. Mixture of Ca sources with TiO2 in certain proportion were ground and calcined at the temperature of 200 °C for 2 hs. Materials were characterized by using X-ray diffractometer (XRD), Fourier Transform-Infra Red (FTIR) and the photocatalytic activity was tested by using methylene blue photooxidation. Perovskite synthesized using CaO derived from snail shell exhibits the similar XRD pattern with that were prepared by using CaO and CaCO3. From the photooxidation activity test, it is proven that CaTiO3 shows similar photocatalytic activity correspond to that were prepared by CaO and CaCO3. Utilazation of shell as agricultural waste of the synthesis of CaTiO3 perovskite is the novelty of this work. Furthermore, the study on material structure and photoactivity is the main focuses for the application in industry and environment.

The Ca-looping process for CO2 capture and energy storage: role of nanoparticle technology

The calcium looping (CaL) process, based on the cyclic carbonation/calcination of CaO, has come into scene in the last years with a high potential to be used in large-scale technologies aimed at mitigating global warming. In the CaL process for CO2 capture, the CO2-loaded flue gas is used to fluidize a bed of CaO particles at temperatures around ~ 650 °C. The carbonated particles are then circulated into a calciner reactor wherein the CaO solids are regenerated at temperatures near ~ 950 °C under high CO2 concentration. Calcination at such harsh conditions causes a marked sintering and loss of reactivity of the regenerated CaO. This main drawback could be however compensated from the very low cost of natural CaO precursors such as limestone or dolomite. Another emerging application of the CaL process is thermochemical energy storage (TCES) in concentrated solar power (CSP) plants. Importantly, carbonation/calcination conditions to maximize the global CaL-CSP plant efficiency could differ radically from those used for CO2 capture. Thus, carbonation could be carried out at high temperatures under high CO2 partial pressure for maximum efficiency, whereas the solids could be calcined at relatively low temperatures in the absence of CO2 to promote calcination. Our work highlights the critical role of carbonation/calcination conditions on the performance of CaO derived from natural precursors. While conditions in the CaL process for CO2 capture lead to a severe CaO deactivation with the number of cycles, the same material may exhibit a high and stable conversion at optimum CaL-CSP conditions. Moreover, the type of CaL conditions influences critically the reaction kinetics, which plays a main role on the optimization of relevant operation parameters such as the residence time in the reactors. This paper is devoted to a brief review on the latest research activity in our group concerning these issues as well as the possible role of nanoparticle technology to enhance the activity of Ca-based materials at CaL conditions for CO2 capture and energy storage.

Low-cost Ca-based composites synthesized by biotemplate method for thermochemical energy storage of concentrated solar power

An ever more environmentally conscious society demands the use of green, sustainable and high-efficiency renewable energy resources. However, large-scale energy storage remains a challenge for a deep penetration of power produced from renewables into the grid. The Calcium-Looping (CaL) process, based on the reversible carbonation/calcination of CaO, is a promising technology for thermochemical energy storage (TCES) in Concentrated Solar Power (CSP) plants. Natural limestone to be used as CaO precursor is cheap, non-toxic and abundant. Nevertheless, recent works have shown that carbonation of CaO derived limestone at optimum conditions for TCES is limited by pore-plugging, which leads to severe deactivation for large enough particles to be employed in practice. In our work, we have synthesized inexpensive CaO/SiO2 composites by means of a biotemplate method using rice husk as support. The morphological and compositional features of the biomorphic materials synthesized help improve the CaO multicycle activity under optimum CSP storage conditions and for particles sufficiently large to be managed in practical processes.

Calcium-Looping performance of steel and blast furnace slags for thermochemical energy storage in concentrated solar power plants

The Calcium Looping (CaL) process, based on the carbonation/calcination of CaO, has been proposed as a feasible technology for Thermochemical Energy Storage (TCES) in Concentrated Solar Power (CSP) plants. The CaL process usually employs limestone as CaO precursor for its very low cost, non-toxicity, abundance and wide geographical distribution. However, the multicycle activity of limestone derived CaO under relevant CaL conditions for TCES in CSP plants can be severely limited by pore plugging. In this work, the alternative use of calcium-rich steel and blast furnace slags after treatment with acetic acid is investigated. A main observation is that the calcination temperature to regenerate the CaO is significantly reduced as compared to limestone. Furthermore, the multicycle activity of some of the slags tested at relevant CaL conditions for TCES remains high and stable if the treated samples are subjected to filtration. This process serves to remove silica grains, which helps decrease the porosity of the CaO resulting from calcination in the mesoporous range thus mitigating pore plugging.

Composition design and performance of alkali-activated cements

In the present work, the relationship between the composition of the SiO2–Al2O3–CaO precursor system and the setting time, microstructure and mechanical properties of the resulting alkali-activated cement (AAC) were investigated. The results showed that with the increase of metakaolin content and the modulus of activator solution, setting time of alkali-activated cements was prolonged. The compressive strength increased with the increase of CaO content to a certain extent, but had different trends as Si/Al ratio varied. Microstructural analyses revealed that CaO content had remarkable effects on the microstructure of AAC. In calcium-free system, the strength was dependent on the three-dimensional structure of N–A–S–H gels. As the CaO content increased gradually, the main activation product changed from N–A–S–H to C–(A)–S–H gel, resulting in a more compact structure. This investigation helps to build up a practical approach for the composition design of alkali-activated cements.

Large-Scale Storage of Concentrated Solar Power from Industrial Waste

Deep penetration of renewable energies into the grid relies on the development of large-scale energy storage technologies using cheap, abundant, and nontoxic materials. Concentrated solar power (CSP) is particularly suitable to massively store thermal energy for dispatchable electricity generation. This is currently accomplished in a few demonstration plants by using molten salts albeit in a not competitive way yet. Process simulation studies indicate that thermochemical energy storage of CSP by means of the calcium looping (CaL) technology would reduce the cost of storage and increase the flexibility of energy supply provided that widely available and cheap CaO precursors with high and stable multicycle activity are used. In this work, we investigate the behavior of calcium rich steel slag at CaL conditions that would expectedly maximize the efficiency of CSP energy storage and power production. When treated with acetic acid, this nontoxic widely abundant waste yields a CaO rich solid with stable convers...

Optimizing the CSP-Calcium Looping integration for Thermochemical Energy Storage

Thermochemical energy storage (TCES) is considered a promising technology to overcome the issues of intermittent energy generation in Concentrated Solar Power (CSP) plants and couple them with yearly electricity demand. The development of this technology could favor the commercial deployment of CSP, which is considered as a key factor for new challenges in reducing GHG emissions. Among other possibilities, using the Calcium Looping (CaL) process for TCES is an interesting choice mainly due to the low cost of natural CaO precursors such as limestone (below $10/ton) and the high energy density that can be achieved (around 3.2GJ/m3). This manuscript explores several configurations in order to maximize the performance of the CSP-CaL integration with the focus on power cycle integration in the carbonator zone. For this purpose, firstly, a discussion about the possibility of using open and closed power cycles is carried out, which leads to the conclusion that a CO2 closed cycle is more appropriate. Then, a closed regenerative CO2 Brayton cycle is analyzed in further detail and optimized by means of the pinch-analysis methodology. A main output is that high plant efficiencies (of about 45%) can be achieved using a simple closed CO2 Brayton power cycle. The optimized integration layout shows good performances at carbonator to turbine outlet pressure ratios around 3, thus allowing for a feasible integration of the power cycle in the CSP-CaL system.

B-doped hardystonite bioceramics from preceramic polymers and fillers: Synthesis and application to foams and 3D-printed scaffolds

Highly porous hardystonite-based bioceramics, in the form of foams and 3D scaffolds, were obtained by the thermal treatment, in air, of silicone resins and engineered micro-sized oxide fillers. Besides CaO and ZnO precursors (CaCO3 and ZnO powders), calcium borate, in both hydrated and anhydrous form (Ca2B6O11·5H2O and Ca2B6O11, respectively), was added to commercial silicone resins, with a significant impact on the microstructural evolution. In hydrated form, calcium borate led to a substantial foaming of silicone-based mixtures, at low temperature (420°C); after dehydration, upon firing, the salt provided a liquid phase, favouring ionic interdiffusion, with the development of novel B-contaning hardystonite-based solid solutions (Ca2Zn1-xB2xSi2-xO7). Although fired at lower temperature than previously developed silicone-derived hardystonite cellular ceramics (950°C, instead of 1200°C), the newly obtained foams and scaffold exhibit substantial improvements in the mechanical properties.

Performance and Carbonation Kinetics of Modified CaO-Based Sorbents Derived from Different Precursors in Multiple CO2 Capture Cycles

Calcium-based sorbent is a suitable sorbent for the solid looping CO2 capture. The loss-in-capacity due to sintering, however, poses a big problem to the direct utilization of natural/pure CaO in the looping process. The issue of attrition, meanwhile, adds a further obstacle to the long-term cyclic utilization of the sorbent. Additionally, the performance of CaO-based sorbent in the long term solid looping CO2 capture depends to a great degree on the type of precursor used to derive the sorbent. This study aims to systematically study the influence of the various calcium precursors on the sorbent performance in the long term carbonation-calcination cycles. Results of this study indicate that the absorption capacity of CaO sorbents was influenced significantly by the type of CaO precursor. It was found that CaO sorbent derived from calcium acetate gave the best absorption capacity of 0.61 mol-CO2/mol-sorbent after 48 carbonation/calcination cycles. The addition of inert supporting matrix of Al2O3 has enhan...

Energy Consumption for CO2 Capture by means of the Calcium Looping Process: A Comparative Analysis using Limestone, Dolomite, and Steel Slag

AbstractThe calcium looping (CaL) process, based upon the dry carbonation/calcination of CaO/CaCO3, is at the center of a potentially low‐cost, second‐generation technology for CO2 capture. This manuscript analyzes the energy penalty that arises from the integration of the CaL process into a coal‐fired power plant using cheap and abundantly available CaO precursors such as natural limestone, dolomite, and steel slag. Experimental results on their multicycle capture capacity behavior obtained from thermogravimetric analysis (TGA) at realistic CaL conditions for CO2 capture are used to this end. This work shows that the specific energy consumption for CO2 avoided (SPECCA) is reduced by using either dolomite or steel slag, whose carbonation kinetics in the diffusive phase are accelerated as compared to limestone. Thus, the use of dolomite as CaO precursor would yield a low SPECCA value of approximately 2 MJ kg−1 CO2 for a residence time of the solids in the carbonator of approximately 10 minutes, which is clearly below the SPECCA value usually reported for conventional amine‐based CO2 capture systems.

Wollastonite-diopside glass-ceramic foams from supercritical carbon dioxide-assisted extrusion of a silicone resin and inorganic fillers

Biphasic ceramics based on wollastonite (CaSiO3) and diopside (CaMgSi2O6) have been recently proposed as valid biomaterials. Silicone resins, filled with inorganic reactive powders, have a great potential in both synthesis of the desired phases and in the shaping in form of highly porous foams. In particular, glass-ceramic foams have been already obtained from a liquid silicone, filled with CaO and MgO precursors and with hydrated salts, such as sodium borate and phosphate. The foaming is due to the release of water vapour within the polymer (at 300–350°C), before its conversion into amorphous silica, and reaction with Ca and Mg oxide, by heat treatment (above 1000°C). In this paper we discuss a significant extension of the approach, referring to a well-known commercial solid silicone. In order to prevent the cross-linking of the silicone (that would compromise the foaming), the polymer and the fillers were mixed by means of conventional polymer extrusion assisted by supercritical carbon dioxide. Finely powdered extrudates could be easily foamed, at 350°C, due to the release of water vapour and CO2. Owing to the uniform cellular structure (with a total porosity of about 80%) and the absence of cracks, the final products, after firing at 1100°C, showed an excellent crushing strength (in the order of 10MPa), far exceeding that of previously developed foams.

Biological influence of Ca/P ratio on calcium phosphate coatings by sol-gel processing

The objective of this work has been to develop low temperature sol-gel glass coatings to modify the substrate surface and to evaluate their bioactivity and biocompatibility. Glasses, based on SiO2·CaO·P2O5, were synthesized by the sol-gel technique using tetraethyl orthosilicate, calcium nitrate tetrahydrate and triethyl phosphate as precursors of SiO2, CaO and P2O5, respectively. Those materials, still in the sol phase, have been used to coat substrates by means of the dip-coating technique. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) has been used for characterize coatings and a microstructural analysis has been obtained using scanning electron microscopy (SEM). The potential applications of the coatings in the biomedical field were evaluated by bioactivity and biocompatibility tests. The coated substrate was immersed in simulated body fluid (SBF) for 21days and the hydroxyapatite deposition on its surface was subsequently evaluated via SEM-EDXS analysis, as an index of bone-bonding capability. In order to study the cell behavior and response to our silica based materials, prepared via the sol-gel method, with various Ca/P ratio and coating substrate, we have used the human osteoblast-like U2OS cell line.

Stability of the Ni–TiO2@nano CaO/Al2O3 complex catalyst used in ReSER process for hydrogen production

This paper describes the preparation and evaluation of a sorption complex catalyst of Ni–TiO2@nano CaO/Al2O3 for hydrogen production by a reactive sorption-enhanced reforming (ReSER) process. TiO2 coating-modified nano CaCO3 as the precursor of nano CaO was prepared by an adsorption phase technique which was able to strictly control the thickness and structure of surface to improve its durability. Ni–TiO2@nano CaO/Al2O3 was prepared by a mixing method which is general mixing that cannot control the content and structure of catalyst. The microstructure was tested by SEM and XRD, and variation in the sorption property of the catalyst was tested by thermogravimetric analysis (TGA). The results showed that TiO2 coating enhanced the stability of the sorption capacity of the catalyst. X-ray diffraction analysis revealed that the TiO2 coating modification inhibited the growth of Ni crystals and prevented CaO and Al2O3 from forming (CaO)12(Al2O3)7 due to the physical isolation by the TiO2 coating of the nano CaCO3. Evaluation of the modified complex catalyst in the ReSER hydrogen production process revealed significant stability for 13 circulations.

ChemInform Abstract: The Calcium‐Looping Technology for CO2 Capture: On the Important Roles of Energy Integration and Sorbent Behavior

AbstractReview: 162 refs.

A new integration model of the calcium looping technology into coal fired power plants for CO2 capture

The Ca-Looping (CaL) process is at the root of a promising 2nd generation technology for post-combustion CO2 capture at coal fired power plants. The process is based on the reversible and quick carbonation/calcination reaction of CaO/CaCO​3 at high temperatures and allows using low cost, widely available and non toxic CaO precursors such as natural limestone. In this work, the efficiency penalty caused by the integration of the Ca-looping technology into a coal fired power plant is analyzed. The results of the simulations based on the proposed integration model show that efficiency penalty varies between 4% and 7% points, which yields lower energy costs than other more mature post-combustion CO2 capture technologies such as the currently commercial amine scrubbing technology. A principal feature of the CaL process at CO2 capture conditions is that it produces a large amount of energy and therefore an optimized integration of the systems energy flows is essential for the feasibility of the integration at the commercial level. As a main novel contribution, CO2 capture efficiency is calculated in our work by considering the important role of the solid-state diffusion controlled carbonation phase, which becomes relevant when CaO regeneration is carried out under high CO2 partial pressure as is the case with the CaL process for CO2 capture. The results obtained based on the new model suggest that integration energy efficiency would be significantly improved as the solids residence time in the carbonator reactor is increased.